In next generation multimedia mobile communication systems, which have been actively studied in recent years, there is a demand for a system capable of processing and transmitting a variety of information (e.g., video and radio data) in addition to the early-stage voice service.
Orthogonal frequency division multiplexing (OFDM) is a multiple-subcarrier modulation scheme in which data transmission is achieved by dividing a frequency band into a plurality of orthogonal subcarriers. The OFDM is one of noticeable core technologies in the next generation multimedia mobile communication systems. Orthogonal frequency division multiple access (OFDMA) provides multi-user multiplexing by combining the OFDM with frequency division multiple access (FDMA) or time division multiple access (TDMA) or code division multiple access (CDMA).
In general, data is transmitted from a base station (BS) to a user equipment (UE), or from the UE to the BS. The data includes user data for a specific UE or a group of UEs and also includes control information. Hereinafter, downlink (DL) represents transmission from the BS to the UE, and uplink (UL) represents transmission from the UE to the BS. The BS and the UE may include a plurality of transmitter and a plurality of receivers. The transmitter codes the data and thus transmits a codeword by mapping the codeword to a plurality of subcarriers. The receiver obtains the codeword for the data by de-mapping a received signal, and then decodes the codeword to obtain original data.
Examples of the control information include a channel quality indicator (CQI) indicating a channel condition, a precoding matrix indicator (PMI) for a multi-antenna system, a rank indicator (RI), etc. Such control information is periodically or occasionally transmitted to facilitate communication between the BS and the UE. The control information can be represented more precisely by increasing a size of a payload of the control information. For example, if 6-bit CQI is transmitted, the CQI can be represented with a maximum of 64 levels, and if 7-bit CQI is transmitted, the CQI can be represented with a maximum of 128 levels, which enables a further accurate representation of the channel condition. However, since radio resources are limited, the amount of radio resources allocated for user data transmission decreases in proportion to the amount of radio resources allocated for control information transmission. Therefore, the radio resources allocated for control information transmission cannot be increased without limitation.
Accordingly, there is a need for a method capable of transmitting more amounts of control information by using limited radio resources.